The field of the present invention relates generally to the delivery of energy impulses (and/or fields) to bodily tissues for therapeutic purposes and more specifically to devices and methods for modulating excitable tissue of the exiting spinal nerves to treat various disorders, such as chronic pain, inflammation and/or other disorders.
Modulation of excitable tissue in the body by electrical stimulation has become an important type of therapy for patients with chronic disabling conditions, including chronic pain, pain associated with cancer, incontinence, problems of movement initiation and control, involuntary movements, vascular insufficiency, heart arrhythmias, obesity, diabetes, craniofacial pain and more. A variety of therapeutic intra-body electrical stimulation techniques can treat these conditions. Typically, such devices include an implantable lead with two or more electrodes attached by a connector to a subcutaneous battery-operated implantable pulse generator (IPG) or other charge storage to provide power and create the electrical impulses carried by hard wire to the lead body containing the electrodes.
Traditional wired leads have several disadvantages, including: a large surgical pocket to house the implantable pulse generator with a battery or charge storage component; extensions and connectors between the IPG and the proximal end of the lead that are housed under the skin, and, a need to recharge or explant the IPG. Having the IPG tethered to the IPG within the patient's body is a disadvantage because this connection can cause lead migration and the possibility for loss of therapy from a disconnection from the IPG exists and has plagued the industry. Placement of an IPG also requires an invasive surgical procedure as the physician must create a pocket of a substantial size of 18 to 75 cc within the body of the patient, typically around the abdomen or buttocks area. Tunneling is also required to connect the classic IPG to the proximal end of the lead located by the targeted nerves. The lead or extension wires must be routed under the skin to reach the classic wired implantable lead. However, devices that utilize a battery-powered or charge-storage component are no longer functional once the battery cannot be recharged or charge cannot be stored. Consequently, for an implanted device, a patient would need to undergo a subsequent surgical procedure to obtain a functional replacement device.
Electrical stimulation of the spinal column and the exiting nerve bundles leaving the spinal cord as a neural modulation therapy and has been used in pain management since the 1970s. Implanted leads containing an electrode array with various polarity settings are used to pass pulsatile waveforms of energy with controllable variations in frequency, pulse width and amplitude. Two or more electrodes are required to be in the array to create an electrical volume conduction area that activates nearby neural structures. The modifications in the parameter settings of the waveform enable the selectively of activating various nerve fibers with different diameters providing various positive therapeutic benefits.
Wired leads for spinal cord stimulation are typically positioned in the epidural space, or through the epidural space, and onto or near exiting nerve bundles. For spinal cord stimulation to be most effective, the volume conduction area of activation must map over the correct dermatomes of the spine. Since most pain can originate from several dermatome levels, one or two wired leads with up to eight electrodes are placed in the epidural space. In cases were two leads are used, the configurations are typically with the leads parallel to each other or at two different vertical locations. The further away from the centerline of the spinal cord within the epidural space, the more specific the nerve recruitment will be for a specific dermatome level. In cases where pain is specific to a certain region, lead placements have been placed closer to the exiting nerve bundle by crossing through the epidural space or by hardwiring with a cut down or other invasive maneuver to the exiting nerve.
Wired leads are associated with numerous failure modes, including, for example, mechanical dislodgement due to motion, acceleration and impingement of the lead electrode assembly, infection and uncomfortable irritation. In particular, longitudinal movement of the lead can move the surface electrodes, making them bear on a different portion of the spinal cord, no longer treating the pain. A transverse or side-to-side movement of the lead can have the same effect, and can also move the electrodes further away from the spinal cord, weakening the signal and/or requiring greater power to reach the targeted nerves. Increased power consumption can decrease battery life, which may require more frequency surgical replacement of the implanted battery.